This application claims foreign priority benefits under 35 U.S.C. 119(a)-(d) of any prior foreign application(s) for patent, inventor""s or plant breeder""s rights certificate(s), or under 365(a)of any PCT application which designated at least one country other than the U.S., listed 29912965.9 filed in Germany on Jul. 24, 1999.
Commercially available injection devices are known from the prior art, in their simplest form as ready-to-use plastic syringes with a syringe barrel, needle assembly with a needle, plunger with a plunger rod, and holding flange, which, as a rule, require skilled handling, especially if a subcutaneous injection is to be performed, i.e., if the needle must first be inserted into a position under the skin that is to be defined as precisely as possible, and only then will the medication be injected.
A device whereby this two-step process can be performed is known (U.S. Pat. No. 3,880,163), wherein drive devices, such as springs and more or less complex guiding devices are disposed within two coaxially: disposed casings, so that the desired two-step process (penetration stroke followed by injection stroke) is ensured sequentially with the push of a button. This device is technically complex and, compared to the syringe itself, takes up excessive space.
It is the object of the invention to attain the above two-step process by means of supplementary devices of a simpler design by which the syringe itself is supplemented.
It is an additional object of the invention that these supplementary devices shall be designed in such a way that a xe2x80x9cmaskingxe2x80x9d of the needle is ensured when it is not in use, i.e., that damage or injuries remain ruled out.
This object is met according to the invention according to the characterizing portion of claim 1.
The underlying concept of the invention thus is that a commercially available syringe is used and a method of operation is selected for the injection device whereby it is ensured that the force exerted onto the plunger rod,:by the patient, either manually or by spring power, is successively first converted into a penetration stroke to reach the subcutaneous injection site, and only then into the injection stroke to inject the medication.
The supplementary devices required for this comprise a coupling element, the function of which is to block a relative movement between the plunger rod and syringe barrel during the penetration stroke, and a guide element in which the syringe is slidably held together, with the coupling element and which has on its inside a trigger mechanism that acts upon the coupling element in such a way that the blocking of the plunger rod is released after the penetration stroke has been performed.
Both additional components, the coupling element and guide element, may be implemented in various design variants, preferably as plastic parts manufactured by injection molding.
With the use of only a few supplementary components, provision can be made for this function mechanism to take place also automatically.
Advantageous embodiments of this principle by means of three variants of the coupling element and guide element are contained in further subclaims.